Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a display screen or a portion thereof with a transitional graphical user interface; and,

FIG. 2 is a front view of a display screen or a portion thereof with a graphical user interface transitioned in sequence from FIG. 1 .

The outer broken-line rectangle shows a display screen or a portion thereof forms no part of the claimed design. The broken-line text and numbers illustrate portions of a graphical user interface and form no part of the claimed design. The areas shown in black tone illustrate a contrast of appearance.

The appearance of the animated graphical interface sequentially transitions from FIG. 1 to FIG. 2 . The process or period in which one image transition to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or a portion thereof with a transitional graphical user interface, as shown and described. 